TRIAC Progress Report - KEK

pure (99.9 %) 12 C target. A monitor SSD was set at 77 cm upstream of the target to
measure elastically backward scattered α particles, whose energies reflect the effective
thickness and uniformity of the irradiated target. Typical beam intensity was 5 µA.
Irradiation times at 0.7 and 1.1 MeV/nucleon are 5 and 2 hours, respectively.
Figure 3-11 shows one of the measured correlation spectra for the energies and the
times-of-flight of detected events by NaI(Tl) detectors. The start trigger of the
time-of-flight measurement was the RF signal (26 MHz) from the TRIAC. The
characteristic γ-rays of about 9 MeV decaying from excited states in 16 O can be found at
around 200 ns as a part of prompt events, which are strongly correlated to the arrival of
the pulsed α-beam. Such prompt events are clearly separated from delayed γ-ray events
starting from around 210 ns; the present observation well demonstrates the successful
operation of the beam pre-bunching system (no beam bunches prior to the main bunch
as shown in Fig. 2-33), otherwise the prompt γ-rays around 9 MeV would be hindered
the delayed γ-rays. Some low-energy, randomly existing γ-rays were also observed,
which indicates that their origin are related to the thermal neutron capture reactions by
the contaminants around target or in detectors (e.g. γ-rays of 6.8 MeV originate from
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I(n, γ) reactions induced by thermal neutrons in the NaI(Tl) detectors). The reaction
cross section will be deduced for those prompt events with γ-ray energy of 9 MeV.
Further analysis is in progress.
3-2. Nuclear and fundamental physics
The following experiments to study nuclear structure and fundamental physics
were carried out using the radioactive ion beams (RIBs) provided by the TRIAC: (1)
RNB-K02/K03: Nuclear spectroscopy through β-delayed decay of spin-polarized nuclei
around doubly magic nucleus 132 Sn (Spokesperson: Y. Hirayama (KEK) and K.
Matsuta (Osaka Univ.), Collaboration: KEK (9), JAEA (6), Osaka Univ. (5), Niigata
Univ. (2), Kochi Univ. of Tech. (1), RIKEN (1)). (2) RNB-K04: Test of time reversal
symmetry using polarized nuclei (Spokesperson: J. Murata (Rikkyo Univ.) and Y.
Hirayama (KEK), Collaboration: Rikkyo Univ. (9), KEK (3), JAEA (2), and RIKEN
(1)). (3) RNB-K08: Search for the highly excited state in 11 Be via 9 Li + d reaction
(Spokesperson: T. Teranishi (Kyushu Univ.) and H. Ishiyama (KEK), Collaboration:
KEK (6), JAEA (7), CNS/Univ. of Tokyo (1), Osaka Univ. (2), and Tsukuba Univ. (1)).
These experiments are respectively summarized in the following subsections. The status
of the RNB-KJ03 (Spokesperson: N. Imai (KEK)), which is to be carried out soon,
will be presented at the end of this section.
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